The present invention relates generally to flexible diaphragms.
More specifically, the present invention constitutes improvements in the diaphragm structure as shown and described in U.S. Pat. No. 2,678,065, in which the reinforcing member comprises a plurality of stacked fabric rubber-coated strips of a ribbon material in which the woven threads are in right-angled relation, the ribbon members being axially stacked with the adjacent strips being successively angularly offset to position the edges of the projecting end portions in overlapped relation.
It has been found that the use of ribbon materials for the reinforcing members requires procedures which are costly and uneconomical. For example, it is uneconomical and time consuming to coat a fabric ribbon of narrow width, such as 11/2-inches. It is also a time consuming and expensive procedure to successively stack the ribbon strips one-by-one in laying up the reinforcing structure prior to the molding operation.
Accordingly, attempts have heretofore been made to provide a more economical and faster procedure for the production of the reinforcing fabric structure than is possible with the single ribbon strips. To this end, it has been proposed that the fabric material should be coated in sheet-roll form, e.g., of a width of more or less 50-inches and thereafer slit the coated sheet to provide the elongate strips for use in place of the ribbon strips as heretofore used. The process of providing slit strips from a wide sheet of fabric material, although cutting down the coating time, presents a problem for the reason that the side edges of the cut strips have a tendency to fray during use. The coating material fails to retain and prevent fraying or dislodgment of the edge threads. Thus, dislodged threads, during use of the diaphragm, have been found to work through the U-shaped surrounding fold and cause leakage. Another concept has also been tried with a view to reducing the time required for coating the ribbon-type fabric, and laying up or stacking of the ribbon elements prior to the molding operation. In this concept, it has been proposed to coat the fabric in roll-sheet form and then die-stamp fabric members of cross-shaped configuration with four projecting radially extending arms having parallel opposite edges, and wherein the woven threads in each arm extends longitudinally and transversely thereof. While this procedure reduces the time required, it still has the undesirable drawback that the edges of the arms were still subject to fraying out, and the threads which extend along the edges could readily become detached during use and provide a potential cause of diaphragm leakage.
According to the present invention, it has been found that the problems as enumerated above can be materially reduced or overcome by coating the fabric material in roll-sheet form, and by changing the configuration of the diepunching from one having arms with parallel edges, to a punching in which the arms radiate from a central portion and have outwardly converging opposite side edges. Similarly, the right-angled threads of the woven fabric are oriented in the punching so that they extend longitudinally and transversely of each arm. As thus arranged, it will be appreciated that there are no edge threads that can become dislodged, and since both the longitudinal and transversely extending threads are severed at an angle along each side of the arm, the severed ends will be securely anchored and fraying will be prevented along the edges of the arms.